1. Field of the Invention
The invention generally relates to a fan and, more particularly, to a fan that can drive air in a radial direction of an impeller thereof.
2. Description of the Related Art
Conventional cooling fans are mainly categorized into two types: an axial-flow type and a blower type. The axial-flow type cooling fan has an axial air inlet and an axial air outlet opposite to the axial air inlet. Air can be drawn via the axial air inlet and then expelled via the axial air outlet. The blower type cooling fan has an axial air inlet in the axial direction, as well as a radial air outlet in the radial direction thereof. Thus, air can be drawn via the axial air inlet and then expelled via the radial air outlet for a cooling operation.
However, the axial-flow type cooling fan must be mounted on a top of an electronic device to be cooled, such as on the top of a Central Processing Unit (CPU) of a computer. This is because the axial-flow type cooling fan can only expel air in the axial direction rather than the radial direction when performing the desired cooling operation. Therefore, the electronic device will have a higher axial height when the axial-flow type cooling fan is mounted thereon. In addition, since the blower type cooling fan draws air via the axial air inlet (in an axial direction) and expels air via the radial air outlet (in a radial direction), the blower type cooling fan cannot be applied to electronic devices that require drawing air from a lateral side thereof (from the radial direction), such as a handset or a Personal Digital Assistant (PDA).
In light of the problems, a conventional fan capable of drawing and expelling air in a radial direction of an impeller was proposed for those electronic devices that require drawing air from the lateral side. Referring to FIG. 1, a conventional fan 8 is disclosed by Taiwan Patent No. 553323 entitled “Fan Structure Having Horizontal Convection”. The conventional fan 8 includes a housing 81 and an impeller 82. The housing 81 is a hollow housing consisting of at least one air inlet 811, at least one air outlet 812, and a radial air channel 813 arranged between the at least one air inlet 811 and the at least one air outlet 812. The impeller 82 is disposed in the radial air channel 813 and includes a hub 821 having a plurality of blades 822 on an outer circumferential face of the hub 821. In such an arrangement, an air pressure difference results between the at least one air inlet 811 and the at least one air outlet 812 when the impeller 82 rotates. The air pressure difference causes air advection between the at least one air inlet 811 and the at least one air outlet 812 for a cooling purpose.
However, when the blades 822 of the impeller 82 cause air to pass through the radial air channel 813, the airflow will be blocked by the hub 821 of the impeller 82 located in the radial air channel 813. Thus, turbulence is caused, and the cooling efficiency of the conventional fan 8 is therefore lowered.
Referring to FIG. 2, Taiwan Patent No. 477492 discloses another conventional fan 9 comprising a rotor seat 91, an impeller 92 and a housing 93. The rotor seat 91 has a plurality of flanges 911, and the impeller 92 has a plurality of grooves 921 engaged with the flanges 911 of the rotor seat 91. The housing 93 can receive the rotor seat 91 and the impeller 92, and has an air inlet 931 and an air outlet 932. In such an arrangement, the impeller 92 can draw air into the housing 93 via the air inlet 931 and expel air via the air outlet 932.
However, the rotor seat 91 and the impeller 92 are also located in an air channel between the air inlet 931 and the air outlet 932. Thus, the airflow caused by the impeller 92 will also be blocked by the rotor seat 91, which causes turbulence. Furthermore, the rotor seat 91 and the impeller 92 are independent components and therefore require assembly. However, it is troublesome to assemble the rotor seat 91 and the impeller 92.